This disclosure relates generally to Tire Pressure Monitoring (TPM), more particularly to locating TPM wheel units with respect to a particular vehicle, and specifically to determining wheel position of tire pressure monitoring wheel units using revolution counter information from the tire pressure monitoring wheel units.
Systems may have been developed to monitor characteristics such as tire pressure and/or tire temperature of a vehicle and to report the characteristics to a receiver at a central monitoring station using radio transmissions. A monitor is located at each tire and periodically takes a measurement of the tire characteristics. The monitor then transmits the results of the measurement in a radio frequency transmission to the central monitoring station which produces an alarm or a display in response to the measurement.
One problem with such systems has been the need to program the location of the transmitters at the central station. To be fully useful, the tire characteristic data is preferably associated with the tire which originated the measurement when presenting a display or alarm. Each monitor typically can transmit unit identification information with the measurement. The tire monitor is preferably activated to produce this information and the information is then conveyed to the central station and associated with the position of the tire.
Existing solutions employed to provide such position information include Radio Frequency Detector (RFD) based systems. These systems employ one or more RFD's to determine which wheel a transmission originates from using received signal strength or other signal attributes. Problematically, such RFD-based systems require cables running from a central receiver to each RFD, typically four RFDs, each located in a wheel arch.
Received Signal Strength Indicator (RSSI) based systems determine front and rear wheel positions by comparing received signal strength from each of the wheel units. Such systems are typically prone to RF power variations and can have problems with attaining a sufficient RF margin between front and rear.
LF (Low Frequency) triggers, typically coils in each wheel arch (or elsewhere nearby) may be employed to activate the wheel unit, which responds in a manner which indicates which LF trigger activated it, thus allowing the receiver to make the wheel position determination in some systems. These systems may have similar problems to those encountered by RFD-based systems.
Many other TPM autolocation systems may use relatively large amounts of power in that the wheel units in such systems transmit more messages or data than typical, and/or include more than the typical components, straining battery resources within the wheel unit.